HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 NUCLEOCAPSID PROTEIN REDUCES REVERSE-TRANSCRIPTASE PAUSING AT A SECONDARY STRUCTURE NEAR THE MURINE LEUKEMIA-VIRUS POLYPURINE TRACT

In an earlier study on minus-strand DNA synthesis catalyzed by murine leukemia virus reverse transcriptase, we described a prominent pause s ite near the polypurine tract (J. Guo, W. Wu, Z. Y. Yuan, K. Post, R. J. Crouch, and J. G. Levin, Biochemistry 34:5018-5029, 1995). We now r eport that pausing at this site is due to a stem-loop structure in the RNA template, formed by interaction of a number of bases in the polyp urine tract, including the six G's, and a 3' sequence which includes f our C's, Addition of human immunodeficiency virus type 1 (HIV-1) nucle ocapsid (NC) protein to reverse transcriptase reactions reduces pausin g by similar to 8- to 10-fold and stimulates synthesis of full-length DNA. Thus, NC functions as an accessory protein during elongation of m inus-strand DNA and increases the efficiency of DNA synthesis, in this case, by apparently destabilizing a region of secondary structure in the template. Since NC is associated with genomic RNA in the viral cor e and is likely to be part df a viral replication complex, these resul ts suggest that NC may also promote efficient DNA synthesis during vir us replication, Mutational analysis indicates that the features of HIV -1 NC which are important for reduction of pausing include the basic a mino acids flanking the first zinc finger, the zinc fingers, and the c ysteine and aromatic amino acids within the fingers. These findings su ggest that reverse transcription might he targeted by drugs which inac tivate the zinc fingers of HIV-1 NC.